Leave your office space unrented and we’ll fine you. That’s the new rule declared by the city of Paris last week. Currently, between six and seven percent of Paris' 18 million square meters of office space is unused, and the city wants to get this vacant office space revamped and occupied by residents. The penalties for unrented space will be as follows: 20 percent of the property’s rental value in the first year of vacancy, 30 percent in the second year and 40 percent in the third year. The plan is to free up about 200,000 square meters of office space for homes, which would still leave a substantial amount of office space available should demand pick up. The city insists that, while the sums involved are potentially large, this isn’t a new tax but an incentive. And, if it has the right effect in getting property re-occupied, may end up being little-used.

Landlords' groups are taking the new plan as well as can be expected. They’ve pointed out that, while the cost of the fines might be high, it could still cost them less to pay them than to convert their properties to homes. According to a property investor quoted in Le Figaro, the cost of transforming an office into apartments can actually be 20 to 25 percent more expensive than constructing an entirely new building. Many landlords might be unwilling or unable to undertake such a process and thus be forced to sell in a market where, thanks to a glut of available real estate, prices are falling. There is also the question of how easy the law will be to enforce: Landlords could rent out vacant properties at a token rent simply to avoid the vacancy fine.

As Paris becomes a laboratory for new legislation to make homes more plentiful and affordable, other European cities would do well to watch it carefully.

It’s too early to see if these predictions will come true, but past experience in smaller French property markets suggests it won’t. The fines have already been introduced elsewhere in France: in the country’s fourth city of Lille (governed by the Socialist party) and in the Parisian satellite town of St Quentin-en-Yvelines (governed by the right wing UMP). So far, neither has experienced a legislation-exacerbated property slump.

It’s also fair to point out that Paris is asking for a round of belt tightening from pretty much every group involved in the city’s real estate. The new levy is part of a plan announced last month that will also pressure state and semi-public bodies to release Parisian land for home building. Paris has some fairly large reserves of this, including space currently owned by the state health authority, by the national railway network and by the RATP—Paris’ transit authority, on whose unused land alone 2,000 homes could be built.

In the meantime, stringent planning laws are also being relaxed to cut development costs for office converters. They will no longer, for example, be obliged to provide parking spaces for new homes, as they had been until the law change. Finally, starting next year, landlords will get an incentive to rent their properties to financially riskier lower-income tenants by having their rents and deposits guaranteed by a new intermediary, a public/private agency called Multiloc. Coming on top of laws that have relaxed building-height restrictions on the Paris periphery, it’s clear that, for Paris developers and landowners, there’s a decent ratio of carrot to stick.

But will it all work? At the very least, Paris deserves recognition for being proactive, especially on a continent where many cities’ grip on the property sector is floundering. Berlin has recently had major new homebuilding plans rejected by residents (for good reason—they were due to get a bad deal), while the U.K.’s number of newly built homes has actually gone down, despite property prices continuing to rise sharply. As Paris becomes a laboratory for new legislation to make homes more plentiful and affordable, other European cities would do well to watch it carefully.